Start with temporary permission, and if you have to, for just a little bit of relaxation and grounding. Repeat it more often if you can. You know how much you can allow yourself at any particular time and the thing to do is to give just a little bit more. It is like stretching; you don't go from being unable to touch your toes to resting your head on your knees instantly. The muscles won't let you do this in one step. It has to be a gradual letting go. That is why temporary permission can be easier to give and accept.

This sounds weird, but you can practice giving permission by giving it to other people in your life. It isn't something you need to say out loud because that might seem weird. Just acknowledge it to yourself that they have earned the right to some relaxation, or grounding, or centering. Tell yourself that they deserve to enjoy good experiences. You probably know some people like that in your life, people you see regularly. When you see them all you have to do is tell yourself that they deserve the good in their lives and maybe even more good than they already have. This works indirectly, but it will help you to also give yourself permission. It is easier if you practice by giving it to other people first. I know it sounds strange, but it does work.